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首页> 外文期刊>Physical review >Non-Hermitian Floquet topological phases: Exceptional points, coalescent edge modes, and the skin effect
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Non-Hermitian Floquet topological phases: Exceptional points, coalescent edge modes, and the skin effect

机译：非麦克尔米特福特拓扑阶段：特殊点，结束边缘模式和皮肤效果

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摘要

Periodically driven non-Hermitian systems can exhibit rich topological band structure and non-Hermitian skin effect, without analogs in their static or Hermitian counterparts. In this work we investigate the exceptional band-touching points in the Floquet quasienergy bands, the topological characterization of such exceptional points and the Floquet non-Hermitian skin effect (FNHSE). Specifically, we exploit the simplicity of periodically quenched two-band systems in one dimension or two dimensions to analytically obtain the Floquet effective Hamiltonian as well as locations of the many exceptional points possessed by the Floquet bulk bands. Two different types of topological winding numbers are used to characterize the topological features. Bulk-boundary correspondence (BBC) is naturally found to break down due to FNHSE, which can be drastically different among different bulk states. Remarkably, given the simple nature of our model systems, recovering the BBC is doable in practice only for certain parameter regime where a low-order truncation of the characteristic polynomial (which determines the Floquet band structure) becomes feasible. Furthermore, irrespective of which parameter regime we work with, we find a number of intriguing aspects of Floquet topological zero modes and π modes. For example, under the open boundary condition, zero edge modes and π edge modes can individually coalesce and localize at two different boundaries. These anomalous edge states can also switch their accumulation boundaries when a certain system parameter is tuned. These results indicate that non-Hermitian Floquet topological phases, though more challenging to understand than their Hermitian counterparts, can be extremely rich in the presence of FNHSE.
机译：定期驱动的非私人系统可以表现出丰富的拓扑带结构和非密封肌肤效果，而无需在静态或赫米特人对应物中的类似物。在这项工作中，我们调查浮子QuasiEnergy乐队中的特殊带接触点，这种特殊点的拓扑表征和浮子非封闭症皮肤效应（FNHSE）。具体地，我们利用一个维度或两个维度的周期性淬火的双频系统的简单性，以分析浮子有效的哈密顿人以及浮子散装带具有所拥有的许多异常点的位置。两种不同类型的拓扑绕组数用于表征拓扑特征。由于FNHSE，自然地发现批量边界对应（BBC）被突破，这在不同散装状态中可能急剧不同。值得注意的是，鉴于我们的模型系统的简单性质，恢复BBC在实践中仅用于某些参数制度，其中特征多项式的低阶截短（确定浮子带结构）变得可行。此外，不管我们使用哪个参数制度，我们发现浮子拓扑零模式和π模式的一些有趣方面。例如，在开放边界条件下，零边缘模式和π边缘模式可以单独聚结，并在两个不同的边界下定位。当调谐某个系统参数时，这些异常边缘状态也可以切换它们的累积边界。这些结果表明，非赫尔米特福特拓扑阶段，虽然比他们的麦克尔尼人对应物更具挑战性，但在Fnhse的存在下可能非常丰富。

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  • 来源
    《Physical review》 |2020年第4期|045415.1-045415.14|共14页
  • 作者

    Xizheng Zhang; Jiangbin Gong;

  • 作者单位

    Department of Physics National University of Singapore Singapore 117551 Republic of Singapore;

    Department of Physics National University of Singapore Singapore 117551 Republic of Singapore;

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